Method for Producing a Multipixel Detector

ABSTRACT

An example includes a method for producing a multipixel detector, the method including: providing a bottom layer including a first and a second bottom electrode, depositing an electrically insulating layer on the bottom layer, forming a first opening through the electrically insulating layer, depositing a first photon absorbing material in the first opening, forming a second opening through the electrically insulating layer, depositing a second photon absorbing material in the second opening, planarizing the deposited electrically insulating layer, the first photon absorbing material, and the second photon absorbing material to form a flat surface, and forming a common top electrode on top of the flat surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a non-provisional patent application claimingpriority to European Patent Application No. 21216902.3, filed Dec. 22,2021, the contents of which are hereby incorporated by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates, in general, to a method for producing amultipixel detector.

BACKGROUND

A multipixel detector comprises several light sensitive pixels whichdetect light. Thus, a multipixel detector may detect an image projectedon the multipixel detector. Each light sensitive pixel of the multipixeldetector may be a photodiode. Thus, a multipixel detector may comprisean array of photodiodes. One type of photodiode is the thin filmphotodiode (TFPD). A TFPD comprises one or more thin film layers,wherein one of the thin film layers comprises a photon absorbingmaterial.

SUMMARY

It is a potential benefit of the present disclosure to provide acost-efficient method for producing multipixel detectors. It is afurther potential benefit of the present disclosure to facilitateproduction of high-quality multipixel detectors. It is a furtherpotential benefit of the present disclosure to prevent lithographicallyrelated damage and/or etch related damage of thin film material duringthe production process. It is a further potential benefit of the presentdisclosure to facilitate production of multipixel detectors with fewdefective pixels, e.g. to facilitate production of multipixel detectorswith few electrically shorted pixels.

According to a first aspect there is provided a method for producing amultipixel detector, the method comprising: providing a bottom layercomprising a first and a second bottom electrode; depositing anelectrically insulating layer on the bottom layer; forming a firstopening through the electrically insulating layer to the first bottomelectrode; depositing a first photon absorbing material in the firstopening to electrically connect to the first bottom electrode; forming asecond opening through the electrically insulating layer to the secondbottom electrode; depositing a second photon absorbing material in thesecond opening to electrically connect to the second bottom electrode;planarizing the deposited electrically insulating layer, the depositedfirst photon absorbing material, and the deposited second photonabsorbing material to form a flat surface, wherein the flat surfacecomprises a top surface of the electrically insulating layer, a topsurface of the first photon absorbing material in the first opening anda top surface of the second photon absorbing material in the secondopening, separated from the top surface of the first photon absorbingmaterial by the top surface of the electrically insulating layer;forming a common top electrode on top of the flat surface, wherein thecommon top electrode electrically connects to the top surfaces of thefirst and second photon absorbing materials in the flat surface; whereinthe common top electrode, the first photon absorbing material in thefirst opening and the first bottom electrode form parts of a first thinfilm photodiode, first TFPD; and the common top electrode, the secondphoton absorbing material in the second opening and the second bottomelectrode form parts of a second thin film photodiode, second TFPD.

The first and second TFPDs may herein respectively function as first andsecond pixels of the multipixel detector.

According to the disclosure, the multipixel detector comprises thin filmphotodiodes. Such photodiodes can be produced in a cost-efficientmanner, e.g. in a more cost-efficient manner than thick film singlecrystalline p-n junctions. Thus, cost-efficient production of themultipixel detector is facilitated by the use of thin film photodiodes.Further, thin film photodiodes may be used in the short-wave infraredwavelength region, e.g. between 1.2 μm and 1.7 μm. Silicon basedphotodiodes may not be compatible with this wavelength range and devicescomprising thick film single crystalline p-n junctions of othermaterials, such as e.g. InAs, may be expensive.

It is a realization that cost-efficient production is furtherfacilitated when the production method for the multipixel detector iscompatible with complementary metal—oxide—semiconductor (CMOS)production methods. CMOS production facilities are abundant.

The method provides a high-quality multiple pixel detector as damage toand/or degradation of the photon absorbing material during processingmay be avoided or reduced. In a multipixel detector, the photonabsorbing material of each pixel should be separated from the photonabsorbing material of the other pixels. If photon absorbing material fora thin film photodetector is lithographically patterned and etched toform separate pixels, as done in the prior art, the photon absorbingmaterial may be damaged and/or degrade. The photon absorbing materialmay e.g. degrade due to lithographically related damage or due to etchrelated damage. Lithographic related damage may be damage caused by heator radiation from the lithographic patterning process, e.g. heat orirradiation from UV-light exposure. Etch related damage may be formationof recombination centers on etched surfaces of the photon absorbingmaterial. It is unfortunate that lithographic patterning and etching,which are commonly used in CMOS production, may cause damage to thephoton absorbing material. However, when the first and second photonabsorbing materials are deposited in the respective first and secondopenings in the electrically insulating layer, the first and secondphoton absorbing materials may be patterned and thereby separated byplanarizing the electrically insulating layer, the first photonabsorbing material, and the second photon absorbing material.

The position and size of the respective first and second openings maydefine the position and size of the respective first and second TFPDs.The position and size of the respective first and second openings (andthus of the first and second TFPDs) may be defined when the first andsecond openings are formed. Forming the first and second openings may bedone through lithographic patterning and etching of the electricallyinsulating layer. However, as some or all of the lithographic patterningand etching steps are performed before depositing photon absorbingmaterial in the openings, degradation of the photon absorbing materialmay be avoided or reduced.

Further, damage to the photon absorbing material during formation of topelectrodes may be avoided as a common top electrode is formed on top ofthe flat surface. Thus, instead of lithographic patterning and etchingindividual top electrodes, a common top electrode may be used.

Further, the method enables use of a common top electrode on top of theflat surface with a reduced risk of electrically shorted pixels, andthereby facilitates production of multipixel detectors with fewdefective pixels. The formation of such a common top electrode mayensure that there is a sufficient distance and electrical insulationbetween the top and bottom electrodes associated with a pixel to preventshort circuits which may result in a defective pixel.

Further, a common top electrode may result in a flat top surface. A flattop surface may be beneficial in many applications. For example, if themultipixel detector is used as part of a focal plane array, a flat topsurface enables focal plane array processing on top of the multipixeldetector.

Further, the method can provide a high-quality multiple pixel detectoras degradation of the photon absorbing material in the finishedmultipixel detector may be avoided or reduced. Depositing the photonabsorbing materials in openings in the electrically insulating layer mayprotect the photon absorbing materials against coming in contact withthe ambient air, e.g. against humidity in the ambient air. In thefinished multipixel detector, the photon absorbing materials may becompletely surrounded by the electrically insulating layer, the bottomelectrode, and the common top electrode.

Due to the nature of the deposition process, the first and second photonabsorbing materials may be in contact with each other before theplanarization. The planarization then forms a flat surface wherein thetop surface of the second photon absorbing material is laterallyseparated from the top surface of the first photon absorbing material bythe top surface of the electrically insulating layer, such that thefirst and second photon absorbing materials are separated from eachother. In other words, when photon absorbing material is deposited in anopening, there may also be photon absorbing material deposited on thetop surface of the electrically insulating layer. The photon absorbingmaterial on the top surface of the electrically insulating layer maythen be removed by the planarization. Planarizing the depositedelectrically insulating layer, the deposited first photon absorbingmaterial and the deposited second photon absorbing material may comprisechemical-mechanical polishing, grinding, and/or fly-cutting.

The multipixel detector may comprise more than a first TFPD and a secondTFPD. The multipixel detector may comprise an array of TFPDs. The arrayof TFPDs may be one-dimensional, e.g. comprise a single row of TFPDs, ortwo-dimensional, e.g. comprise rows and columns of TFPDs. The multipixeldetector may be part of an imaging device.

As will be described further below, the first and second photonabsorbing materials may be, or comprise, the same material or differentmaterials, e.g. materials with different absorption peak wavelengths.The first and second openings may be formed simultaneously orseparately. The first and second photon absorbing materials may bedeposited simultaneously or separately.

The first and second photon absorbing materials may have the samethickness or different thicknesses. For example, the thickness of thefirst and/or second photon absorbing materials may depend on the quantumefficiency of the photon absorbing material.

The common top electrode may be at least partially transparent to light.

Each pixel of the multipixel detector, e.g. each of the first and secondpixels, may be configured to absorb a photon, such as a photon which haspassed through a transparent common top electrode, by the photonabsorbing material and thereby generate a photogenerated electron-holepair in the photon absorbing material. Thus, each TFPD of the multipixeldetector may be configured to absorb photons. Each TFPD of themultipixel detector may be configured to separate the electron and thehole of the photogenerated electron-hole pair and either: in a so called“hole to read-out” (h2ro) configuration, deliver the hole to the bottomelectrode for read-out and the electron to the common top contact, or ina so called “electron to read-out” (e2ro) configuration, deliver theelectron to the bottom electrode for read-out and the hole to the commontop contact.

The first and second TFPDs may each comprise a bottom charge carriercontrol layer between the photon absorbing material and the bottomelectrode and/or a top charge carrier control layer between the photonabsorbing material and the common top electrode, wherein each of thebottom and top charge carrier control layers of the first and secondTFPDs comprise at least one of: an electron transport layer, a holetransport layer, an electron blocking layer, a hole blocking layer, anelectron injection layer, or a hole injection layer.

The charge carrier control layers may be configured to facilitateseparation of electrons and holes of photogenerated electron-hole pairs.This may be done by tuning (or bridging) the work function of the bottomelectrode with respect to the work function of the photon absorbingmaterial and/or tuning (or bridging) the work function of the common topelectrode with respect to the work function of the photon absorbingmaterial.

An electron transport layer may be a layer configured to enhanceelectron transport from the photon absorbing material to the adjacentelectrode.

A hole transport layer may be a layer configured to enhance holetransport from the photon absorbing material to the adjacent electrode.

An electron blocking layer may be a layer configured to block electrontransport from the photon absorbing material to the adjacent electrode.

A hole blocking layer may be a layer configured to block hole transportfrom the photon absorbing material to the adjacent electrode.

An electron injection layer may be a layer configured to enhanceelectron injection to the photon absorbing material.

A hole injection layer may be a layer configured to enhance holeinjection to the photon absorbing material.

The bottom charge carrier control layer and top charge carrier controllayer may be configured to promote transport of opposite types of chargecarriers. As an example, if the bottom charge carrier control layer isan electron transport layer, the top charge carrier control layer may bea hole transport layer. As another example, if the bottom charge carriercontrol layer is a hole transport layer, the top charge carrier controllayer may be an electron transport layer.

The method may further comprise depositing a bottom charge carriercontrol layer in the first opening before depositing the first photonabsorbing material in the first opening, such that the first bottomelectrode and side walls of the first opening are covered by the bottomcharge carrier control layer, and/or depositing a bottom charge carriercontrol layer in the second opening before depositing the second photonabsorbing material in the second opening, such that the second bottomelectrode and side walls of the second opening are covered by the bottomcharge carrier control layer.

When the bottom charge carrier control layer is deposited in an openingthrough the electrically insulating layer, the bottom charge carriercontrol layer may not need to be lithographically patterned and etched.Thus, lithographically related damage and/or etch related damage to thebottom charge carrier control layer may be avoided or reduced, inanalogy to the above discussion related to the photon absorbingmaterial.

To illustrate, the first and second bottom electrodes may first beformed by depositing a layer of electrode material, e.g. metal. Thelayer of electrode material may then be patterned and etched into thefirst and second bottom electrodes after which the electricallyinsulating layer is deposited, the openings formed, and the bottomcharge carrier control layer is deposited in an opening. Thus, thebottom charge carrier control layer may not need to be subjected to thepatterning and etching of the layer of electrode material.

To cover side walls of an opening, the bottom charge carrier controllayer may be deposited with a conformal depositing technique.

When a bottom charge carrier control layer is deposited in an opening,the method may further comprise forming an electrically insulatingbarrier on the flat surface formed by planarizing the depositedelectrically insulating layer, the deposited first photon absorbingmaterial, and the deposited second photon absorbing material, theelectrically insulating barrier covering a part of a bottom chargecarrier control layer deposited in the first or second opening, whereinthe covered part of the bottom charge carrier control layer lies withinthe flat surface.

Planarizing the deposited electrically insulating layer, the depositedfirst photon absorbing material, and the deposited second photonabsorbing material may also include planarizing parts of the bottomcharge carrier control layer which have been deposited on the topsurface of the electrically insulating layer and thereby remove thoseparts. However, after planarization there may be parts of the bottomcharge carrier control layer within the flat surface. If a top chargecarrier control layer or a common top electrode is deposited onto suchparts of the bottom charge carrier control layer within the flatsurface, charge carriers may bypass the photon absorbing material and adefective pixel may be formed. Thus, it may be beneficial to provide anelectrically insulating barrier covering the part of a bottom chargecarrier control layer that lies within the flat surface. Thereby,defective pixels may be avoided or reduced. In particular, whendepositing a common top electrode afterwards, the electricallyinsulating barrier may provide electrical insulation between the commontop electrode and the bottom charge carrier control layer, such thatdefective pixels may be avoided or reduced.

The method may, as an alternative or addition to depositing a bottomcharge carrier control layer in an opening, comprise: providing a bottomcharge carrier control layer on the first bottom electrode beforedepositing the electrically insulating layer; and/or providing a bottomcharge carrier control layer on the second bottom electrode beforedepositing the electrically insulating layer.

Thus, as an alternative to depositing a bottom charge carrier controllayer in an opening, the bottom charge carrier control layer may beprovided on a bottom electrode before depositing the electricallyinsulating layer. For example, the bottom charge carrier control layermay be deposited onto the layer of electrode material and patterned andetched together with the layer of electrode material. The bottom chargecarrier control layer may not necessarily be as sensitive tolithographically related damage and/or etch related damage as the photonabsorbing layer, at least in some situations. Further, depositing thebottom charge carrier control layer before depositing the electricallyinsulating layer may simplify the processing of the multipixel detector.

The method may further comprise forming a common top charge carriercontrol layer configured such that the common top electrode electricallyconnects to the top surfaces of the first and second photon absorbingmaterials in the flat surface via the common top charge carrier controllayer, wherein the common top charge carrier control layer is formedafter planarizing the deposited electrically insulating layer, thedeposited first photon absorbing material, and the deposited secondphoton absorbing material. Thus, damage to the photon absorbing materialduring formation of top charge carrier control layers may be avoided asa common top charge carrier control layer is formed on top of the flatsurface. Thus, instead of lithographic patterning and etching individualtop charge carrier control layers, a common top charge carrier controllayer may be used.

It should be understood that in some situations individual top chargecarrier control layers may be used.

Some photon absorbing materials may be particularly sensitive tolithographically related damage and/or etch related damage. Suchmaterials may be PbS quantum dots, InAs quantum dots, and/or organicsemiconductors. Thus, the first or second photon absorbing materials maycomprise PbS quantum dots, InAs quantum dots, and/or an organicsemiconductor. In this case, the potential benefits in terms offacilitating a high-quality of the multipixel detector may beparticularly large.

As previously mentioned, the multipixel detector may comprise a CMOScircuit. For example, the bottom layer may comprise a complementarymetal—oxide—semiconductor, CMOS, readout integrated circuit, wherein theCMOS readout integrated circuit comprises CMOS electronic circuitsconfigured to convert an amount of charge carriers from the respectivefirst and second TFPDs into respective electrical signals when themultipixel detector is in operation.

As previously mentioned, the first and second photon absorbing materialsmay be, or comprise, different materials, e.g. materials with differentabsorption peak wavelengths. Thus, an absorption peak wavelength of thefirst photon absorbing material is different from an absorption peakwavelength of the second photon absorbing material.

The absorption peak wavelength may be the wavelength at which photonabsorption is strongest, e.g. the wavelength where the absorptioncoefficient of the photon absorbing material is largest.

When the first and second photon absorbing materials have differentabsorption peak wavelengths they may absorb photon in differentwavelength bands. Thus, the multipixel detector may be seen as amultispectral detector, also known as a multispectral sensor.

The multispectral detector may comprise more than a first TFPD and asecond TFPD. The multispectral detector may be configured to absorbphotons in more than two different wavelength bands, e.g. more than 5different wavelength bands, or more than 10 different wavelength bands.The multispectral detector may comprise an array of TFPDs. The array ofTFPDs may be one-dimensional, e.g. comprise a single row of TFPDs, ortwo-dimensional, e.g. comprise rows and columns of TFPDs. Themultispectral detector may be a multispectral imaging device.

For a multispectral detector it may be beneficial to perform at leastsome of the processing of TFPDs with different photon absorbingmaterials separately. For example, it may be beneficial to at leastpartially form a TFPD with one photon absorbing material before startingto process a TFPD with another photon absorbing material. Thus, theTFPDs that are formed first may be subjected to many iterations oflithographic patterning and therefore subjected to heat and/or radiationfrom the lithographic patterning process many times in conventionalmethods. Therefore, the use of planarization and a common top contact toreduce the number of lithographic patterning processes the photonabsorbing materials of the TFPDs are subjected to may be particularlybeneficial for a multispectral detector.

The method may comprise configuring the multipixel detector such thatthe first bottom electrode is arranged at a first distance from thecommon top electrode and the second bottom electrode is arranged at asecond distance from the common top electrode, wherein the seconddistance is smaller than the first distance. Different distances betweenthe common top electrode and the respective first and second bottomelectrodes may be used to individually tune the absorption for the firstand second TFPDs. This may be useful when the first and second photonabsorbing materials are the same. It may be particularly useful when thefirst and second photon absorbing materials are different, e.g. when thefirst and second photon absorbing materials have different quantumefficiencies.

The method may comprise configuring the multipixel detector such thatthe first bottom electrode is arranged at a first distance from thecommon top electrode and the second bottom electrode is arranged at asecond distance from the common top electrode, wherein the seconddistance is smaller than the first distance and wherein a quantumefficiency of the second photon absorbing material is larger than aquantum efficiency of the first photon absorbing material.

Thus, the larger quantum efficiency of the second photon absorbingmaterial may be partially or fully compensated by the smaller distancebetween the second bottom contact and the common top contact, ascompared to the distance between the first bottom contact and the commontop contact. Thereby, the absorption for the first and second TFPDs maybe tuned such that their saturation times are similar. Thus, ahigh-quality multispectral detector may be enabled. If the first andsecond TFPDs would have the same distance between the bottom contact andthe common top contact but very different quantum efficiencies, one TFPDwould saturate much faster than the other.

The method may further comprise depositing a sacrificial layer, whereinthe sacrificial layer is deposited between the deposition of the firstand second photon absorbing materials, such that the first and secondphoton absorbing materials are separated by the sacrificial layer; andremoving the sacrificial layer in the planarization step.

Such a sacrificial layer may protect the photon absorbing material whichis deposited first. For example, the photon absorbing material which isdeposited first may be protected from intermixing with the photonabsorbing material which is deposited later.

The sacrificial layer may be deposited after the deposition of the firstphoton absorbing material and before the forming of the second opening.Thus, the first photon absorbing material may be protected from etchrelated damage during etching of the second opening. The first photonabsorbing material may also be protected from other damage duringforming of the second opening.

The method may further comprise: planarizing, in an intermediateplanarization step, the deposited electrically insulating layer and thedeposited first photon absorbing material, wherein the intermediateplanarization step is carried out after depositing the first photonabsorbing material in the first opening, and before forming the secondopening through the electrically insulating layer.

When the second opening is formed after depositing the first photonabsorbing material in the first opening it may be beneficial to use anintermediate planarization step such that the patterning resolution forforming the second opening does not degrade due to an uneven surface ora surface that lies above the top surface of the electrically insulatinglayer.

The method may be configured such that the first opening is formed suchthat a top part of the first opening is larger than a bottom part of thefirst opening, whereby the first opening is tapered, and/or the secondopening is formed such that a top part of the second opening is largerthan a bottom part of the second opening, whereby the second opening istapered.

A tapered opening makes it easier to fully fill the opening and avoidpockets without photon absorbing material in the opening.

BRIEF DESCRIPTION OF THE FIGURES

The above, as well as additional, features will be better understoodthrough the following illustrative and non-limiting detailed descriptionof example embodiments, with reference to the appended drawings.

FIG. 1 illustrates a multipixel detector, according to an example.

FIG. 2 illustrates a flat surface after planarization, according to anexample.

FIG. 3 is a flow chart of a method, according to an example.

FIG. 4 a is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 4 b is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 4 c is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 4 d is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 4 e is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 4 f is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 4 g is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 4 h is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 4 i is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 4 j is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 4 k is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 41 is part of a time sequence of illustrations showing a multipixeldetector during production, according to an example.

FIG. 5 a is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 5 b is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 5 c is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 5 d is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 5 e is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 5 f is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 5 g is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 5 h is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 6 is a flow chart of a method, according to an example.

FIG. 7 a is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 7 b is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 7 c is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 7 d is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 7 e is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 7 f is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 7 g is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 7 h is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 7 i is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 7 j is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 7 k is part of a time sequence of illustrations showing amultipixel detector during production, according to an example.

FIG. 71 is part of a time sequence of illustrations showing a multipixeldetector during production, according to an example.

FIG. 8 illustrates a multipixel detector, according to an example.

All the figures are schematic, not necessarily to scale, and generallyonly show parts which are necessary to elucidate example embodiments,wherein other parts may be omitted or merely suggested.

DETAILED DESCRIPTION

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings. That which is encompassed by theclaims may, however, be embodied in many different forms and should notbe construed as limited to the embodiments set forth herein; rather,these embodiments are provided by way of example. Furthermore, likenumbers refer to the same or similar elements or components throughout.

FIG. 1 illustrates a multipixel detector 10 which may be producedaccording to the method 100 of the disclosure. The illustratedmultipixel detector 10 has a bottom layer 20 comprising a CMOS readoutintegrated circuit 24, a first bottom electrode 21, and a second bottomelectrode 22. The first bottom electrode 21 and the second bottomelectrode 22 are arranged on a bottom insulator 26 on top of the CMOSreadout integrated circuit 24 and connected to the CMOS readoutintegrated circuit 24 by via connections 28 going through the bottominsulator 26. The first bottom electrode 21 and the second bottomelectrode 22 are embedded in an electrically insulating layer 30. Afirst opening 31 and a second opening 32 go through the electricallyinsulating layer 30 to the first bottom electrode 21 and the secondbottom electrode 22 respectively. The first opening 31 is at leastpartially filled with a first photon absorbing material 41. Similarly,the second opening 32 is at least partially filled with a second photonabsorbing material 42.

The first photon absorbing material 41 in the first opening 31 iselectrically connected to the first bottom electrode 21 by a bottomcharge carrier control layer 71 between the first photon absorbingmaterial 41 and the first bottom electrode 21. Similarly, the secondphoton absorbing material 42 in the second opening 32 is electricallyconnected to the second bottom electrode 22 by a bottom charge carriercontrol layer 71 between the second photon absorbing material 42 and thesecond bottom electrode 22. Further, both the first photon absorbingmaterial 41 and the second photon absorbing material 42 are electricallyconnected to a common top electrode 60 by a top charge carrier controllayer 72 which in the illustration is a common top charge carriercontrol layer.

According to the above: the common top electrode 60, the first photonabsorbing material 41 in the first opening 31, and the first bottomelectrode 21 form parts of a first TFPD 11. Further, the common topelectrode 60, the second photon absorbing material 42 in the secondopening 32 and the second bottom electrode 22 form parts of a secondTFPD 12.

In the following, examples of materials that may be used in themultipixel detector 10 will be given.

The first bottom electrode 21 and the second bottom electrode 22 maycomprise metal, e.g. aluminium, copper, tantalum nitride, or titaniumnitride.

The common top electrode 60 may be at least partially transparent. Thecommon top electrode 60 may comprise indium tin oxide (ITO), indiumgallium zinc oxide (IGZO), or graphene.

Examples of photon absorbing materials that may be used are PbS quantumdots, InAs quantum dots, and/or other quantum dots. The quantum dots maybe colloidal quantum dots. Thus, a photon absorbing material may be acolloidal quantum dot thin film. Further examples of photon absorbingmaterials that may be used are organic semiconductors and/or perovskitematerial. The first photon absorbing material 41 and the second photonabsorbing material 42 may be, or comprise, the same material.Alternatively, the first photon absorbing material 41 and the secondphoton absorbing material 42 may be, or comprise, different materials.For example, the first photon absorbing material 41 and the secondphoton absorbing material 42 may be materials with different absorptionpeak wavelengths. For example, the first photon absorbing material 41may comprise one type of quantum dots and the second photon absorbingmaterial 42 may comprise another type of quantum dots, such that thephoton absorbing materials have different absorption peak wavelengths.Alternatively, the first photon absorbing material 41 and the secondphoton absorbing material 42 may comprise the same type of quantum dotswhere the quantum dots of the first photon absorbing material 41 have adifferent size compared to the quantum dots of the second photonabsorbing material 42, such that the photon absorbing materials havedifferent absorption peak wavelengths. Further, the first photonabsorbing material 41 and the second photon absorbing material 42 may bematerials of different types. For example, the first photon absorbingmaterial 41 may comprise quantum dots and the second photon absorbingmaterial 42 may comprise an organic semiconductor material.

A bottom charge carrier control layer 71 may comprise at least one of:an electron transport layer, a hole transport layer, an electronblocking layer, a hole blocking layer, an electron injection layer, or ahole injection layer.

Similarly, a top charge carrier control layer 72 may comprise at leastone of: an electron transport layer, a hole transport layer, an electronblocking layer, a hole blocking layer, an electron injection layer, or ahole injection layer.

The bottom charge carrier control layer 71 and the top charge carriercontrol layer 72 may be configured to promote transport of oppositetypes of charge carriers. In one configuration, the bottom chargecarrier control layer 71 is an electron transport layer and the topcharge carrier control layer 72 is a hole transport layer. In anotherconfiguration, the bottom charge carrier control layer 71 is a holetransport layer and the top charge carrier control layer 72 is anelectron transport layer.

Examples of an electron transport layer that may be used are TiO₂ andNiobium Oxide (NbO_(x)).

Examples of a hole transport layer that may be used are nickel oxide(NiO)x and copper oxide (CuO_(x)).

The electrically insulating layer 30 may be silicon oxide, siliconnitride, or aluminum oxide.

FIG. 3 illustrates a flow chart of a method 100 for producing amultipixel detector, such as the multipixel detector 10 of FIG. 1 . Themethod 100 will herein be described in conjunction with FIGS. 4 a-l .FIGS. 4 a-l show a time sequence of illustrations of the multipixeldetector 10, seen in cross-section, during production according to theflow chart of FIG. 3 . In the example given, all steps of the method 100shown in FIG. 3 will be included.

A bottom layer 20 comprising a first bottom electrode 21 and a secondbottom electrode 22 is provided S102, as illustrated in FIGS. 4 a-c .FIGS. 4 a-c illustrate how a bottom layer 20 may be manufactured. Thefirst bottom electrode 21 and a second bottom electrode 22 may bearranged on a readout circuit. In FIG. 4 a CMOS readout integratedcircuit 24 is used. The CMOS readout integrated circuit 24 is shown inFIG. 4 a but excluded from FIGS. 4 b-l for clarity. A bottom insulator26 is arranged on top of the CMOS readout integrated circuit 24 and viaconnections 28 going through the bottom insulator 26 are formed, asshown in FIG. 4 a . A layer of bottom electrode material may then bedeposited on the bottom insulator 26 (comprising the via connections 28)followed by a bottom charge carrier control layer 71, as seen in FIG. 4b . Subsequently, the first bottom electrode 21 and the second bottomelectrode 22 may be formed out of the layer of bottom electrode materiale.g., by patterning and etching. The bottom charge carrier control layer71 may simultaneously be patterned and etched. Thus, in the method 100the bottom charge carrier control layers 71 on the first bottomelectrode 21 and the second bottom electrode 22 are provided S103 beforedepositing S104 the electrically insulating layer 30, as shown in FIG. 4c . The electrically insulating layer 30 is subsequently deposited S104on the bottom layer 20, as seen in FIG. 4 d . The electricallyinsulating layer 30 may be a silicon oxide, silicon nitride, or aluminumoxide layer. The electrically insulating layer 30 may be deposited e.g.,through physical vapor deposition, chemical vapor deposition, orspin-coating.

The electrically insulating layer 30 may then be planarized, as seen inFIG. 4 e . Planarizing the electrically insulating layer 30 may improvethe resolution of forthcoming patterning steps.

A first opening 31 through the electrically insulating layer 30 to thefirst bottom electrode 21 is then formed S106, as seen in FIG. 4 f . Thefirst opening 31 may be formed through patterning, e.g. lithographicpatterning and etching.

A first photon absorbing material 41 is then deposited S108 in the firstopening 31 to electrically connect to the first bottom electrode 21, asseen in FIG. 4 g . The first photon absorbing material 41 maysimultaneously be deposited on a top surface of the electricallyinsulating layer 30. The first photon absorbing material 41 may comprisePbS quantum dots, InAs quantum dots, other quantum dots, an organicsemiconductor, and/or perovskite. The first photon absorbing material 41may be deposited through e.g. spin coating, printing, physical vapordeposition, or evaporation.

FIG. 4 h illustrates an intermediate planarization step wherein thedeposited electrically insulating layer 30 and the deposited firstphoton absorbing material 41 are planarized S110. The intermediateplanarization step may form a flat surface comprising a top surface ofthe electrically insulating layer 30 and a top surface of the firstphoton absorbing material 41 in the first opening 31.

FIG. 4 i illustrates a step wherein a sacrificial layer 45 is depositedS112. In the illustrated example the sacrificial layer 45 is depositedS112 on the surface formed by the intermediate planarization step.

A second opening 32 through the electrically insulating layer 30 to thesecond bottom electrode 22 is then formed S114, as seen in FIG. 4 j .The second opening 32 may be formed through patterning, e.g.lithographic patterning and etching.

A second photon absorbing material 42 is then deposited S116 in thesecond opening 32 to electrically connect to the second bottom electrode22, as seen in FIG. 4 k . The second photon absorbing material 42 maysimultaneously be deposited on a top surface of sacrificial layer 45, asillustrated. Thus, the sacrificial layer 45 may separate the firstphoton absorbing material 41 and the second photon absorbing material42. If a sacrificial layer 45 is not used, the second photon absorbingmaterial 42 may simultaneously be deposited on a top surface of theelectrically insulating layer 30.

The second photon absorbing material 42 may comprise PbS quantum dots,InAs quantum dots, other quantum dots, an organic semiconductor, and/orperovskite. The second photon absorbing material 42 may be depositedthrough e.g. spin coating, printing, evaporation, or physical vapordeposition.

The electrically insulating layer 30, the first photon absorbingmaterial 41, and the second photon absorbing material 42 are thenplanarized S118 to form a flat surface 50, as seen in FIG. 41 . Thereby,in the example shown, the sacrificial layer 45 is also removed S120. Theflat surface 50 comprises a top surface 56 of the electricallyinsulating layer 30, a top surface 51 of the first photon absorbingmaterial 41 in the first opening 31, and a top surface 52 of the secondphoton absorbing material 42 in the second opening 32, separated fromthe top surface 51 of the first photon absorbing material 41 by the topsurface 56 of the electrically insulating layer 30.

Any of the planarization steps described in the examples above and belowmay comprise chemical-mechanical polishing and/or grinding and/orfly-cutting.

FIG. 2 illustrates a top view of the flat surface 50, in this case fromwhat is intended to be a multipixel device comprising a 4 by 4 array ofTFPDs. Thus, in the flat surface 50 there can be seen a row comprising afirst opening 31, a second opening 32, a third opening 33, and a fourthopening 34 which are respectively filled with a first photon absorbingmaterial 41, a second photon absorbing material 42, a third photonabsorbing material 43, and a fourth photon absorbing material 44. InFIG. 2 there are in total four rows which each may have the samecombination of photon absorbing material as the previously describedrow, as illustrated. The flat surface 50 comprises a top surface 56 ofthe electrically insulating layer 30, a top surface 51 of the firstphoton absorbing material 41 in the first opening 31, and a top surface52 of the second photon absorbing material 42 in the second opening 32,separated from the top surface 51 of the first photon absorbing material41 by the top surface 56 of the electrically insulating layer 30.Further, each top surface of photon absorbing material in an opening isseparated from the other top surfaces of photon absorbing material bythe top surface 56 of the electrically insulating layer 30.

As seen in FIG. 41 , the sacrificial layer 45 may be removed S120 in theplanarization step S118 or in conjunction with the planarization stepS118.

As shown in FIG. 1 , subsequently a top charge carrier control layer 72may be formed S121. A common top electrode 60 is formed S122 thatelectrically connects to the top surface 51 and the top surface 52 ofthe first photon absorbing material 41 and the second photon absorbingmaterial 42 in the flat surface 50. FIG. 1 may herein be seen as thefinished multipixel detector 10 after depositing the top charge carriercontrol layer 72 and the common top electrode 60 on the flat surface 50shown in FIG. 41 .

It should be understood that the steps of the method 100 may notnecessarily be performed in the order described in conjunction withFIGS. 3-4 . Further, in some instances some steps may be performedsimultaneously. This is exemplified in FIGS. 5 a-h which are a timesequence of illustrations showing a multipixel detector duringproduction, wherein the first photon absorbing material 41 and thesecond photon absorbing material 42 of the multipixel detector comprisesthe same material.

FIG. 5 a illustrates a bottom layer 20 comprising a first bottomelectrode 21 and a second bottom electrode 22 being provided S102.

FIG. 5 b illustrates an electrically insulating layer 30 being depositedS104 on the bottom layer 20.

FIG. 5 c illustrates a planarization of the electrically insulatinglayer 30.

FIG. 5 d illustrates the first opening 31 and the second opening 32being formed S106, S114 through the electrically insulating layer 30 tothe first bottom electrode 21 and the second bottom electrode 22,wherein the openings are formed simultaneously. For example, the firstopening 31 and the second opening 32 may be defined in the samelithographic patterning step and/or etched simultaneously.

FIG. 5 e illustrates that in this example the first photon absorbingmaterial 41 and the second photon absorbing material 42 are the samematerial. FIG. 5 e further illustrates the first photon absorbingmaterial 41 and the second photon absorbing material 42 being depositedS108, S116. Thus, in this example the first photon absorbing material 41and the second photon absorbing material 42 are depositedsimultaneously.

FIG. 5 f illustrates the electrically insulating layer 30, the firstphoton absorbing material 41, and the second photon absorbing material42 after being planarized S118 to form a flat surface 50.

FIG. 5 g illustrates a top charge carrier control layer 72 being formedS121.

FIG. 5 h illustrates a common top electrode 60 formed S122 on top of thetop charge carrier control layer 72. Thus, the common top electrode 60is also formed S122 on top of the flat surface 50.

In the above examples, a bottom charge carrier control layer 71 has beenprovided S103 on the first bottom electrode 21 and the second bottomelectrode 22 before deposition S104 of the electrically insulating layer30. Alternatively, or additionally, a bottom charge carrier controllayer 71 may be deposited S107 in the first opening 31 before depositingS108 the first photon absorbing material 41 in the first opening 31and/or a bottom charge carrier control layer 71 may be deposited S107 inthe second opening 32 before depositing S116 the second photon absorbingmaterial 42 in the second opening 32. This will be shown below in amethod 100 according to the flow chart of FIG. 6 . The method 100 willherein be described in conjunction with FIG. 7 . FIGS. 7 a-l show a timesequence of illustrations of the multipixel detector 10, seen incross-section, during production according to the flow chart of FIG. 6 .In the example given, the steps of the method 100 will be included. Inthe example, the first photon absorbing material 41 and the secondphoton absorbing material 42 are the same material. However, theexemplified method 100 is applicable also in the case when the firstphoton absorbing material 41 and the second photon absorbing material 42are different materials as well as when the first opening 31 and secondopening 32 opening are formed separately.

According to the illustrated method 100, a bottom layer 20 comprising afirst bottom electrode 21 and a second bottom electrode 22 is providedS102, see FIG. 7 c .

FIGS. 7 a-c illustrate how a bottom layer 20 may be manufactured. Thefirst bottom electrode 21 and a second bottom electrode 22 may bearranged on a readout circuit. In FIG. 7 a a CMOS readout integratedcircuit 24 is used. The CMOS readout integrated circuit 24 is shown inFIG. 7 a but excluded from FIGS. 7 b-l for clarity. A bottom insulator26 is arranged on top of the CMOS readout integrated circuit 24 and viaconnections 28 going through the bottom insulator 26 are formed, asshown in FIG. 7 a . A layer of bottom electrode material may bedeposited on the bottom insulator 26, as shown in FIG. 7 c .Subsequently, the first bottom electrode 21 and the second bottomelectrode 22 may be formed out of the layer of bottom electrode materiale.g. by patterning and etching the layers, as shown in FIG. 7 c ,whereby the bottom layer 20 is provided S102.

The electrically insulating layer 30 is subsequently deposited S104 onthe bottom layer 20, as seen in FIG. 7 d .

FIG. 7 e illustrates a planarization of the electrically insulatinglayer 30.

FIG. 7 f illustrates the first opening 31 and the second opening 32being formed S106, S114 through the electrically insulating layer 30 tothe first bottom electrode 21 and the second bottom electrode 22,wherein the openings are formed simultaneously. For example, the firstopening 31 and the second opening 32 may be defined in the samelithographic patterning step and/or etched simultaneously.

Further, in this example a bottom charge carrier control layer 71 isdeposited S107 in the first opening 31 and in the in the second opening32, as seen in FIG. 7 g . In this example, it is the bottom chargecarrier control layer 71 which is simultaneously deposited into bothopenings. The bottom charge carrier control layer 71 may conformallycoat the surface, i.e., it may be deposited by a conformal coatingtechnique. Thus, the first bottom electrode 21 and the second bottomelectrode 22 as well as the side walls of the first opening 31 and thesecond opening 32 may be covered by the bottom charge carrier controllayer 71, as illustrated. The surface may then be planarized, as seen inFIG. 7 h.

FIG. 7 i illustrates that in this example the first photon absorbingmaterial 41 and the second photon absorbing material 42 are the samematerial. FIG. 7 i further illustrates the structure after depositionS108, S116 of the first photon absorbing material 41 and the secondphoton absorbing material 42, in this example being the same material,and planarization S118 to form a flat surface 50. After planarizationS118 a part 74 of the bottom charge carrier control layer 71 may liewithin the flat surface 50. If a top charge carrier control layer 72and/or a common top electrode 60 would be formed on top of the part 74of the bottom charge carrier control layer 71 a defective pixel could beformed. This may e.g. be avoided by the formation of an electricallyinsulating barrier 46.

In this example, an electrically insulating barrier 46 is formed S124 onthe flat surface 50, as seen in FIG. 7 j . An electrically insulatingbarrier material may be deposited as a layer and patterned and etched toform opening to the first photon absorbing material 41 and the secondphoton absorbing material 42, as also seen in FIG. 7 j . The patterningmay be such that the part 74 of a bottom charge carrier control layer 71lying within the flat surface 50 is covered.

FIG. 7 k illustrates a top charge carrier control layer 72 being formedS121.

FIG. 7 l illustrates a common top electrode 60 formed S122 on top of thetop charge carrier control layer 72. Thus, the common top electrode 60is also formed S122 on top of the flat surface 50.

FIG. 8 illustrates a multipixel detector wherein the first bottomelectrode 21 is arranged at a first distance from the common topelectrode 60 and the second bottom electrode 22 is arranged at a seconddistance from the common top electrode 60, wherein the second distanceis smaller than the first distance. Herein the quantum efficiency of thesecond photon absorbing material 42 may be larger than the quantumefficiency of the first photon absorbing material 41. The first bottomelectrode 21 and the second bottom electrode 22 with different heightmay be implemented in any of the above given examples. FIG. 8 furtherillustrates the first opening 31 and the second opening 32 beingtapered. Tapered openings may be implemented in any of the above givenexamples.

It should be understood that the method 100 may comprise further stepsthan the ones described above. For example, after forming the common topelectrode 60, the multipixel detector may be further processed to form afocal plane array.

While some embodiments have been illustrated and described in detail inthe appended drawings and the foregoing description, such illustrationand description are to be considered illustrative and not restrictive.Other variations to the disclosed embodiments can be understood andeffected in practicing the claims, from a study of the drawings, thedisclosure, and the appended claims. The mere fact that certain measuresor features are recited in mutually different dependent claims does notindicate that a combination of these measures or features cannot beused. Any reference signs in the claims should not be construed aslimiting the scope.

What is claimed is:
 1. A method for producing a multipixel detector, themethod comprising: providing a bottom layer comprising a first bottomelectrode and a second bottom electrode; depositing an electricallyinsulating layer on the bottom layer; forming a first opening throughthe electrically insulating layer to the first bottom electrode;depositing a first photon absorbing material in the first opening toelectrically connect to the first bottom electrode; forming a secondopening through the electrically insulating layer to the second bottomelectrode; depositing a second photon absorbing material in the secondopening to electrically connect to the second bottom electrode;planarizing the electrically insulating layer, the first photonabsorbing material, and the second photon absorbing material to form aflat surface, wherein the flat surface comprises a top surface of theelectrically insulating layer, a top surface of the first photonabsorbing material in the first opening, and a top surface of the secondphoton absorbing material in the second opening separated from the topsurface of the first photon absorbing material by the top surface of theelectrically insulating layer; and forming a common top electrode on topof the flat surface, wherein the common top electrode electricallyconnects to the top surfaces of the first photon absorbing material andthe second photon absorbing material on the flat surface, wherein thecommon top electrode, the first photon absorbing material in the firstopening, and the first bottom electrode form parts of a first thin filmphotodiode (TFPD), and wherein the common top electrode, the secondphoton absorbing material in the second opening, and the second bottomelectrode form parts of a second TFPD.
 2. The method according to claim1, wherein the first TFPD comprises a bottom charge carrier controllayer between the first photon absorbing material and the first bottomelectrode and a top charge carrier control layer between the firstphoton absorbing material and the common top electrode.
 3. The methodaccording to claim 2, wherein the second TFPD comprises the bottomcharge carrier control layer between the second photon absorbingmaterial and the second bottom electrode and the top charge carriercontrol layer between the second photon absorbing material and thecommon top electrode.
 4. The method according to claim 3, wherein eachof the bottom charge carrier control layer and the top charge carriercontrol layer comprises an electron transport layer, a hole transportlayer, an electron blocking layer, a hole blocking layer, an electroninjection layer, or a hole injection layer.
 5. The method according toclaim 4, wherein the method comprises: depositing the bottom chargecarrier control layer in the first opening before depositing the firstphoton absorbing material in the first opening, such that the firstbottom electrode and side walls of the first opening are covered by thebottom charge carrier control layer.
 6. The method according to claim 5,further comprising depositing the bottom charge carrier control layer inthe second opening before depositing the second photon absorbingmaterial in the second opening, such that the second bottom electrodeand side walls of the second opening are covered by the bottom chargecarrier control layer.
 7. The method according to claim 5, wherein themethod comprises forming an electrically insulating barrier on the flatsurface formed by planarizing the electrically insulating layer, thefirst photon absorbing material, and the second photon absorbingmaterial, the electrically insulating barrier covering a part of thebottom charge carrier control layer deposited in the first opening orthe second opening, wherein the part of the bottom charge carriercontrol layer lies within the flat surface.
 8. The method according toclaim 3, wherein the method comprises: providing the bottom chargecarrier control layer on the first bottom electrode before depositingthe electrically insulating layer.
 9. The method according to claim 8,further comprising providing the bottom charge carrier control layer onthe second bottom electrode before depositing the electricallyinsulating layer.
 10. The method according to claim 3, wherein themethod comprises: forming a common top charge carrier control layerconfigured such that the common top electrode electrically connects tothe top surfaces of the first photon absorbing material and the secondphoton absorbing material in the flat surface via the common top chargecarrier control layer, wherein the common top charge carrier controllayer is formed after planarizing the electrically insulating layer, thefirst photon absorbing material, and the second photon absorbingmaterial.
 11. The method according to claim 1, wherein planarizing theelectrically insulating layer, the first photon absorbing material, andthe second photon absorbing material comprises chemical-mechanicalpolishing, grinding, and/or fly-cutting.
 12. The method according toclaim 1, wherein the first photon absorbing material or the secondphoton absorbing material comprises PbS quantum dots, InAs quantum dots,and/or an organic semiconductor.
 13. The method according to claim 1,wherein the bottom layer further comprises a complementarymetal—oxide—semiconductor, (CMOS) readout integrated circuit, whereinthe CMOS readout integrated circuit comprises CMOS electronic circuitsconfigured to convert an amount of charge carriers from the first TFPDand the second TFPD into electrical signals.
 14. The method according toclaim 1, wherein a first absorption peak wavelength of the first photonabsorbing material is different from a second absorption peak wavelengthof the second photon absorbing material.
 15. The method according toclaim 1, wherein the first bottom electrode is arranged at a firstdistance from the common top electrode and the second bottom electrodeis arranged at a second distance from the common top electrode, whereinthe second distance is smaller than the first distance.
 16. The methodaccording to claim 15, wherein a quantum efficiency of the second photonabsorbing material is larger than a quantum efficiency of the firstphoton absorbing material.
 17. The method according to claim 1, furthercomprising: depositing a sacrificial layer between deposition of thefirst photon absorbing material and deposition of the second photonabsorbing material, such that the first photon absorbing material andthe second photon absorbing material are separated by the sacrificiallayer, wherein planarizing the electrically insulating layer comprisesremoving the sacrificial layer.
 18. The method according to claim 1,further comprising: planarizing, in an intermediate planarization step,the electrically insulating layer and the first photon absorbingmaterial, wherein the intermediate planarization step is carried outafter depositing the first photon absorbing material in the firstopening, and before forming the second opening through the electricallyinsulating layer.
 19. The method according to claim 1, wherein the firstopening is formed such that a top part of the first opening is largerthan a bottom part of the first opening, whereby the first opening istapered.
 20. The method according to claim 19, further comprising thesecond opening is formed such that a top part of the second opening islarger than a bottom part of the second opening, whereby the secondopening is tapered.